266 THEORETICAL BIOLOGY 



while in the genesis of individuals we may also assume a pro- 

 gressive genolysis. Both lead to similar results by methods 

 that are wholly in accord with plan. Just as the final products 

 of the germ, the completed somatic cells, are at once more 

 differentiated and poorer in potentialities than are the germ- 

 cells, so are the species that have arisen by splitting off 

 more differentiated and less rich than is the mother-species. 

 J All of this concerns merely the increase of complexity in 

 the phenotype, but tells us nothing about its increase in the 

 genotype. The genotype can become richer only through 

 new genes arising ; and as to this we know nothing. 

 Kammerer's experiments, which are intended to prove that 

 new genes do arise, certainly give interesting preliminaries 

 for elucidating this problem, but are far from containing 

 sufficient evidence for the settling of anything so far-reaching. 



It is also possible to take up another attitude, and suppose 

 that new genes do not arise at all, and that it is only the 

 melody of the impulse-sequence that changes. If we compare 

 the genes to the keys of a piano, it is obvious that all tunes 

 can be played with relatively little material substance. If 

 we assume that in the germ of the first living organism were 

 present all the ferments necessary to effect all the changes 

 in form and substance that we observe in the development, 

 we might maintain that the difference between the forms 

 of animals from that time until now depends merely on the 

 fact that only a limited number of ferments were used by the 

 primitive impulse-sequence of the first organism. In course 

 of time, the impulse-melodies became richer and more in 

 tricate, so as to create at last the symphony of the Mammalia. 



At the same time, perhaps, in consequence of the splitting 

 off of species, the originally complete keyboard lost more 

 and more of its notes, so that in animals at the present day 

 the possibility of shaping new melodies diminishes as the 

 melodies are developed. 



